The purpose of this study is to measure cerebral blood flow with positron emission tomography (PET) and H215O during a short-term (declarative) verbal memory task in patients with posttraumatic stress disorder (PTSD) and healthy subjects. The hippocampus is felt to play an important role in short-term verbal memory. Previous PET studies have shown activation of the hippocampus with short-term declarative verbal memory tasks. We have previously shown smaller hippocampal volume and deficits in short- term declarative verbal memory function in patients with combat-related as well as severe childhood abuse-related PTSD. The current project will extend these studies by examining function of the hippocampus in patients with PTSD. We hypothesize that PTSD patients will have a blunted hippocampal blood flow response to short-term verbal (declarative) memory tasks relative to controls.